Tricycle Design- ENGR 201 Group Orientation

Transcription

1 Tricycle Design- Electrical l Components ENGR 201 Group Orientation

2 Outline Electric Tricycle Component Overview Basic DC Motor Theory Operation Motor Sizing Common o DC Motor Types Brushed Brushless DC Motor Speed Control Resistive Pulse Width Modulation Operator Interface (Motor Controller Input) DC Motor Directional Control Batteries Basic Theory Common Battery Types Battery Interconnection: Series/Parallel

3 Electric Tricycle Project Objective Bring increased mobility to disabled persons in Burkina Faso by providing an appropriate, cost effective method of retrofitting the existing hand- powered tricycle with an electric power train and controls.

4 Electric Tricycle-- Component Overview user inputs

5 Electric Tricycle-- Component Overview User Interface (Controller Input) Power Interrupt and Battery Voltage Forward & Reverse Control Power Distribution (under seat) DC Motor & Controller Batteries Battery Enclosure

6 Basic DC Motor Theory Q: The flow of electrons (current) through a wire inherently produces what? A: A circular magnetic field perpendicular A: A circular magnetic field perpendicular to the direction of current flow.

7 Basic DC Motor Theory: Simplified Brushed PM Motor Circuit Current is applied to the wire loop via a commutator Current is applied to the commutator via graphite brushes. The brushes ride against the commutator to provide a rotating electrical connection Actual motors have a large # of wire loops (windings) wrapped around an iron core at varying angles. This group of windings and core make up the motor armature or rotor. Each wire loop has a corresponding set of segments on the commutator The fixed magnets in the picture make up the stator or motor field. An actual motor may have several pairs of permanent magnets (PM) making up the field. Electromagnets replace permanent magnets in the stator in many motor designs.

8 Brushless Motor Brushless motors have the windings attached to the motor case. Permanent magnets are attached to the armature (rotor) Brushless motors work by electronically switching the motor current on and off in the different windings to vary the magnetic field so there is no need for a commutator and brushes. Brushless Motor Diagram The two main types: Sensored: Uses small dedicated sensors inside the motor housing to sense the position and movement of the armature. Motor operates with dedicated control configured. Sensorless: Advanced electronics and software allow for current control without dedicated sensors. This technology allows you to select the controller and motor separately for peak performance based on application.

9 Brushed vs. Brushless Motors Brushless Motors Pros Dissipate heat better because the windings are attached to the motor housing Have a very high torque to inertia ratio on interior rotors only Have a very high peak torque (on interior rotors) Very high reliability (no commutator or brush to wear out) Generally higher efficiency due to the elimination of friction between the brush and commutator. Brushless Motor Cons Require sophisticated control More expensive than comparable brushed motors

10 Motor & Control Currie Scooter Motor 24V, PM, Brushed Type 600 W 2600 RPM 24V PWM Type Control 0-5V Input 40 A Output Environmentally Sealed Complete kit $ $60.00

11 Motor Output Power Formula General Formula P = Tω where P= Output Power T= Output Torque ω=output Speed

12 Motor Output Power Formula P (watts)= Torque (in-oz) x Speed (rpm) 1352 Conversion: 746 watts=1 HP

13 Motor Output Output power components: Kinetic Energy: rotational speed (rpm) Potential Energy: torque (ft-lbs, oz-ins) Conservation of energy; for a given amount of power: As speed increases torque must decrease As torque increases speed must decrease Manufacturer/Vendor Data Rules of Thumb: DC Brushless Motors Rules of Thumb: Motor Sizing

14 Motor Output For all DC motors, the speed is nearly proportional to the supply voltage. For permanent magnet DC motors the output torque or load is proportional to the input current. The higher the load the higher the current draw.

15 DC Motor Control Resistive Control Voltage drop across a resistor : V=IR Series voltages add/subtract Add resistance in series with the motor to reduce motor operating voltage. Pros & Cons Simple & Inexpensive Very Inefficient Multiple p circuit branches for multiple speeds

16 DC Motor Control Pulse Width Modulation Switches (pulses) power to the motor on and off very quickly, motor notices the average effect The frequency and width of the pulses dictates motor output. As the relative amount of time that the voltage is on increases compared with the amount of time that it is off, the average speed of the motor increases. Pros & Cons Pros & Cons Efficient Relatively Inexpensive Not field repairable

17 Operator Interface PWM Controller Input= 0-5V DC Stock Controller: Twist Throttle Sold State Hall Effect Sensor

18 Operator Interface PWM Controller Input= 0-5V DC Redesigned Controller: 50 K Rotary Potentiometer Audio Taper

19 DC Motor Directional Control The rotational direction of a DC motor can be changed by switching The rotational direction of a DC motor can be changed by switching the polarity of the input power at the motor terminals.

20 Battery Types Primary (Non Rechargeable) Secondary (Rechargeable) Flooded Sealed (VRLA) Gel Cells AGM Starter Type Deep Cycle Type

21 Batteries Sizing: i Potential- Volts Typical Cell Voltage ~2V Capacity- Amp Hours Related to Cell Size

22 Battery Interconnection Series Adds Voltage Parallel l Adds Current +24V 12 Volt, 210 AH 12Volt, 210 AH 210 AH

23 System Wiring Diagram